A spectroscopic experimental and semi-empirical study of [Eu (salen)2] as a red-emitter for phosphor-converted UV LED

Most of commercial WLEDs have a lack of red-emission component resulting in cool white illumination. Aiming this issue, in this paper, we present the synthesis of [Eu(salen)2] with a Schiff base type ligand, the salen (N,N '-ethylene-bis(salicylidenimine)), another lanthanide complex was also investigated, the [Gd(salen)2]. Both complexes were characterized by conventional spectroscopy techniques to confirm their preparation, and the free software LUMPAC was used as a friendly interface to determine the experimental intensity parameters (omega 2 and omega 4) for the Eucomplex, it was also used to optimize the complex structure, perform theoretical calculations of excited states, and intensity parameters. The Eu-complex was immobilized in PMMA films in different amounts, and their photophysics properties were analyzed. The 7.5 wt% doped film showed the best photophisical results (r = 0.226 ms; phi EuEu = 9.61%), and it was chosen to coat a UV LED-chip (lambda em = 400 nm +/- 10 nm) to fabricate a red emissive LED-prototype; also, a prototype with a blend between powdered Eu-complex and cyanoacrylate glue was fabricated, and their emission behavior and radiant photostability were compared. The prototype with the doped PMMA film exhibited poorer radiant photostability than the powder prototype after 24 h of operation. Thus, the [Eu(salen)2] powder prototype gather some important characteristics to be used as a red component of warm WLEDs.

Automated summary

This paper presents the synthesis of [Eu(salen)2] and [Gd(salen)2] complexes to address the lack of red-emission component in commercial WLEDs. Experimental results show that immobilizing the Eu complex in PMMA films can be used to manufacture a red emissive LED prototype, although the doped PMMA film prototype exhibited slightly poorer radiant photostability compared to the powder prototype.